This invention relates to surface acoustic wave (SAW) devices and, in particular, to high density SAW channelizers having relatively high frequency resolution with minimal cross-talk (high isolation) and high surface utilization.
Signal channelizers provide means for dividing a broad band signal into a plurality of narrow contiguous frequency segments which may be viewed simultaneously. Channelizers are especially useful in RF receivers adapted for electronic warfare. Channelized receivers however suffer from some important deficiencies. Some are excessively large and heavy and consume excessive amounts of power. One of the problems with channelized structures is isolation of the various signals in the incoming RF signal. Cross-talk creates noise problems which can diminish the dynamic range and efficiency of the system. Cross-talk occurs, for example, because acoustic signals propagate in all directions across the surface of the substrate thereby affecting adjacent transducers at the output. This problem has been somewhat alleviated by systems in which a curved input transducer consisting of an array of subtransducers of the same frequency focuses waves at a plurality of output transducers each tuned to a different frequency. The output transducers are selectively located at focal points formed where all the individual contributions add up in phase. However, signal dispersion occurs because the acoustic wave signal propagates in multi-mode fashion. Electromagnetic noise or interference also occurs because of the close spacing of elements or the substrate.